The production of nitrogen by the cryogenic rectification of feed air is a well established commercial process. Typically, nitrogen is produced by rectification of the feed air in a single column cryogenic rectification plant wherein a portion of the waste fluid is turboexpanded to generate refrigeration to drive the separation. The portion of the waste fluid which is not turboexpanded constitutes an inherent thermodynamic irreversibility and thus a source of inefficiency.
Nitrogen demand is increasing especially for such uses as blanketing and inerting in the metalworking and electronics industry and for nitrogenation in the chemical industry. Accordingly it is desirable to improve the nitrogen recovery which is attainable with the conventional cryogenic rectification system. This is particularly the case where nitrogen product is desired at an elevated pressure such as at a pressure greater than about 80 psia since it is known that cryogenic rectification is more difficult at higher pressures due to the reduced relative volatilities of the components to be separated.
Accordingly, it is an object of this invention to provide a cryogenic rectification system whereby nitrogen may be produced with an improved recovery over that attainable with conventional systems.